During the past year work on this project has mainly involved studies of the immune response to leishmanial infections in patients with different clinical forms of the disease. The survey for cases of diffuse cutaneous leishmaniasis (DCL) in Mexico, which began last year, yielded parasite isolates from 6 DCL cases and 4 from patients with regular cutaneous leishmaniasis (CL). One isolate was L. b. braziliensis, which we believe has not been found before in Mexico; the others were all members of the L. mexicana complex. Since both ulcerative CL and the unusual anergic type of DCL, caused by apparently the same species of organism, occur in the same geographic area, it would appear to be the best area to study host factors responsible for DCL. Four patients with CL and one new Mexican DCL patient were studied at the Clinical Center. Cryopreserved peripheral blood mononuclear (PBM) cells from regular CL cases were found to give essentially the same proliferative responses a fresh cells. In contrast, cryopreserved PBM cells from a DCL case showed a different pattern, in keeping with our suspicions that the cells responsible for suppression in DCL are more susceptible to damage or destruction by freezing than are most other PBMs. However, more observations on DCL patients are needed to be certain of this conclusion. Collaborative studies have been initiated with Dr. Ponce in Honduras of an unusual form of cutaneous leishmaniasis due to L. donovani chagasi, the species of parasite normally causing visceral leishmaniasis in Latin America. 16 cases (9 parasitologically confirmed) have occurred in an island community where kala azar has also been present.